1. Field of the Invention
The present invention relates to a direct drive guide unit performing guidance of relative motion that is used in mechanisms that perform linear relative motion in, for example, machine tools and industrial robots.
2. Description of the Prior Art
An example of this type of direct drive guide unit of the prior art is indicated in FIG. 1.
As indicated in FIG. 1, said direct drive guide unit has steel track rail 1, in which tracks in the form of a pair of track grooves 1a are formed in both the right and left sides along the lengthwise direction, two rolling element circulating paths (to be later described in detail) corresponding to each of said track grooves 1a, and a slider in the form of sliding unit 2 able to move relative to said track rail 1. A plurality of rolling elements in the form of balls 3, that bear the load by circulating while rolling along the above-mentioned track groove 1a accompanying movement of sliding unit 2, are arranged and contained within said rolling element circulating paths.
Sliding unit 2 has casing 5, straddled across track rail 1, a pair of end caps 6 and 7 coupled to both ends of said casing 5, and two seals 8 and 9 mounted on the outside surface of each said end cap 6 and 7. Furthermore, casing 5 and end caps 6 and 7 are made of a metal such as steel. Each above-mentioned rolling element circulating path is composed of two sets of load bearing track groove 5a and return path 5b, each formed linear and mutually in parallel with both the left and right ends of casing 5, roughly semi-circular direction changing paths (not shown) that connect both ends of said load bearing track groove 5a and return path 5b, formed in both end caps 6 and 7. Furthermore, the above-mentioned loading bearing track groove 5a is in opposition to track groove 1a of track rail 1.
The above-mentioned direct drive guide unit of the prior art has the shortcomings described below.
(1) Formation of the above-mentioned rolling element circulating paths and assembly of the unit is not always easy, and there are a large number of parts. PA1 (2) Since the members that perform relative operation are made of metal, together with the noise produced during operation being relatively large, providing of lubricating oil must be performed frequently. PA1 (3) Rust forms easily and there is poor resistance to chemicals and so forth. PA1 (4) Since the unit has a high degree of magnetic permeability, it is easily subjected to magnetism. PA1 (5) Due to the large mass, the unit has large inertia and its response to applied driving force is not favorable.